= Mass spectrometer detector
A <mass spectrometer detector> turns arriving <ions> into a recorded electrical <signal>. It is distinct from the <mass analyzer> that makes <mass-to-charge ratio> information distinguishable. The measured response can depend on collection, conversion and amplification as well as on how many ions arrived.
A <Faraday cup> collects <electric charge> directly. Ideally, a flux $\Phi$ of ions with known charge $q$ gives $I=q\Phi$. For $10^6$ singly charged positive ions per second, the current is $1.602176634\times10^{-13}\,\mathrm A$, about $0.1602\,\mathrm{pA}$. Escaping <secondary electrons> and background currents must be accounted for when inferring particle delivery.<Faraday Cup by the ALPHA experiment>[Experiment description, collected charge and particle counting]{ref}
An <electron multiplier> instead uses secondary emission to amplify the initial conversion signal. The manufacturer's detector description shows discrete <dynodes>, a continuous-dynode alternative, and a conversion dynode before the multiplier.<Detector by Shimadzu>[Detector overview, electron multiplication and conversion-dynode sections]{ref} In an illustrative equal-stage model, ten stages with mean yield $\delta=4$ give mean gain $G=4^{10}=1048576$. This is a model calculation, not a measured gain for a named instrument.
<Detector gain> and <detection efficiency> answer different questions: the size of an output event and the probability of registering an arriving ion. Increasing gain cannot recover missed ions. At high signals, <mass spectrometer detector saturation> can also invalidate proportionality between ion delivery and recorded response. Quantitative peak comparisons therefore need a tested response range and appropriate <instrument calibration>, not merely a large signal.
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